Internal combustion engines have at least one cylinder head connected to a cylinder block in such a manner that the pair can form at least one combustion chamber, or cylinder. Within the cylinder, combustion gasses are discharged via exhaust openings while the chamber is filled with air via inlet openings that allow charge air from an intake manifold to be drawn into the chamber. With respect to a charge change, the cylinder head is therefore subjected to a high thermal and mechanical load as it reciprocates within the chamber to transform combustion energy into rotational motion of the crankshaft. In addition, due to an increasing integration of components within the engine bay the packing of components is becoming increasingly dense so the demands on the cylinder head are also increasing.
In this context, an increasing proportion of engines are charged by means of exhaust turbochargers and/or mechanical chargers in order to power all of the components within the engine. As such, the thermal load on the engine or cylinder head rises further so higher demands are made on the cooling system. In response, measures are taken to influence the thermal balance of the internal combustion engine to prevent a thermal overload of the engine.
When an engine includes an air cooling system, the engine may include a fan to dissipate heat by means of an air flow guided over the surface of the engine. However, because fluids have a higher thermal capacity compared to air, liquid cooling systems allow substantially greater heat quantities to be dissipated than is possible with air cooling. For this reason combustion engines under high thermal load are usually equipped with liquid cooling.
With regard to the design of engine cooling systems, maximum cooling demand is commonly found in order to ensure adequate cooling of the engine under all operating conditions. However, the result of this is an engine cooling system that is over-dimensioned in relation to normal operation, that is, in relation to the average cooling demand. Therefore, the cooling power of the engine is designed for operating states characterized by high loads with simultaneously low vehicle speeds, for example operating conditions that correspond to acceleration and hill climbing, to prevent overheating of the engine while supplying the required cooling power under the least favorable conditions. Under such conditions the engine cooling system dissipates a very large quantity of heat without the availability of air flow. In addition, under certain circumstances, high ambient temperatures can further aggravate the problem of providing adequate cooling power.
When the engine cooling system is designed in a manner that accommodates the scenario described above, large coolers or heat exchangers result that are difficult to accommodate in the front-end region of a vehicle. But, due to a limited amount of space available, this presents difficulties since enlarging the radiator is not an option as further heat exchangers, in particular cooling devices, are also included to ensure secure fault-free operation of the engine or to optimize the operation of the engine. Therefore, an inclusion of overly-large radiator may severely restrict the arrangement and dimensions of other heat exchangers within the engine compartment.
In one example, engines are known that are fitted with a multiplicity of heat exchangers designed with sufficiently large heat-transmitting area to fulfill their function. However, because of the limited space available in an engine system, conflicts arise between the size and arrangement of individual heat exchangers in the front-end region. Therefore, in some embodiments, radiators are arranged in line, spaced apart and overlap partly. In addition, flow guide plates may be included to direct or guide the flow of air through the engine compartment.
In another example, cooling systems are known that have powerful fan motors to drive, or set in rotation, a fan wheel in order to provide a sufficiently high mass air flow to heat exchangers within the cooling system. The fan motors are usually driven electrically and can support the heat transmission in the heat exchangers at any operating point, even when the motor vehicle is stationary or stopped, or when the vehicle operates at low vehicle speeds.
In yet another example, radiators with two fans are known wherein a higher cooling power results from two fans that can cover a larger area than a single fan or single fan wheel. In this context, a radiator for liquid cooling has particular significance as this radiator ensures safe operation of the internal combustion engine by dissipating large quantities of heat. Nonetheless, further measures are required to limit the thermal load of internal combustion engines even under the least favorable circumstances.
To prevent thermal overloads of an engine, methods to control the charge pressure on the intake side of the engine as a function of the coolant temperature TCoolant, the charge air temperature TCharge and/or the rotation speed of the engine are known. In particular the charge pressure is lowered if the coolant temperature, TCoolant, the charge air temperature, TCharge and/or the rotation speed of the internal combustion engine reaches, exceeds, or falls below a predefined value. However, this derating method has disadvantages since the reduction of charge pressure also leads to a reduced engine power. Therefore, the heat input into the engine is lowered by reducing the engine power. In certain circumstances, though, a reduction in engine power is not acceptable. For example, a driver of a motor vehicle must have the power demanded on acceleration or on hill climbing, not just for comfort reasons but in some cases also from safety aspects.
The inventors herein have recognized the above issues, as well as limitations of such approaches. In this context, the methods described include of influencing the thermal balance of an engine in a manner that reduces the thermal load of an engine without substantially reducing the output power provided by the engine.
One example method includes determining at least one of a charge air temperature TCharge, a coolant temperature TCoolant and/or the ratio value ηignition,act/ηignition,opt, wherein ηignition,act is an efficiency of the engine system at a momentary ignition timing point and ηignition,opt is an efficiency of the engine system at the optimized ignition timing point. Then, in response to one or more of these values, a control system may reduce an air ratio (e.g., air-fuel ratio) λ as a function of an input variable. For example, if TCharge is greater than the upper limit temperature, TCharge,up, the air ratio λ may be reduced as a function of TCharge.
Therefore, according to the example method, the air ratio λ is reduced as a function of an input parameter within the system wherein the fuel-air mixture is enriched to reduce the thermal load of the engine without substantially reducing the power to the engine. In particular, the method allows the reduction of the heat input even in demanding driving situations, while at the same time maintaining the driving speed or charge pressure and hence the power.
Within the context of the present disclosure, the engine system described encompasses diesel engines, spark-ignition engines and also hybrid internal combustion engines. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.